The present invention relates to a high frequency coupler for coupling two high frequency elements, and also to plasma processing apparatus and method which utilize plasma generated by using high frequency electric power for fabrication of electronic devices, such as semiconductors, micro-machines, and the like.
FIG. 7 is a sectional view of an etching apparatus carrying an antenna system plasma source which has been already proposed by us. Referring to FIG. 7, when evacuation is carried out by a pump 3 operative as an evacuation device while a predetermined gas is introduced from a gas feeder 2 into a vacuum chamber 1, and when high-frequency electric power is supplied from a high frequency antenna power source 4 to an antenna 6 on a dielectric window 8 via a matching circuit 5 and a high frequency coupler 107 for coupling the matching circuit 5 to the antenna 6 while a predetermined pressure is maintained in the vacuum chamber 1, plasma is generated within the vacuum chamber 1 to enable plasma processing, such as etching, depositing, and surface modification, to be carried out with respect to a substrate 10 placed on a substrate electrode 9. In this case, as FIG. 7 shows, by supplying high frequency electric power to the substrate electrode 9 from a high frequency power source 11 for the substrate electrode, it is possible to control ion energy that would reach the substrate 10.
The high frequency coupler 107 is a coupler formed from a copper plate and, in case that the high frequency electric power to be supplied to the antenna is of a large magnitude, plural copper plates, superposed one over another, are used in order to increase the electric current capacity. The reason why a copper plate material comprised of copper plates placed one over another is preferred rather than a copper plate having its thickness merely increased is that high frequency provides a skin effect. That is, a high frequency current tends to flow only in the uppermost surface of a conductor and, therefore, in order to allow a large current flow, it is necessary to increase the surface area of the conductor.
However, the conventional system shown in FIG. 7 involves the problem of poor plasma uniformity.
The configuration of the copper plate is such that the copper plate is poorly symmetric in relation to the center of the antenna and, therefore, a current distribution will occur on the antenna under the influence of the electric current flowing in the copper plate. That is, the distribution of electric current flowing in the antenna shows such a non-uniformity as illustrated in FIG. 8. In order to uniformize the distribution of current, it is better that a cylindrical high-frequency coupler is us ed instead of the copper plate. In that case, however, there is a problem that the surface area of the high frequency coupler is too small to allow a large current flow.
Such a phenomenon as above mentioned is not a phenomenon which can be seen only with a plasma processing apparatus carrying a plasma source of antenna system. A similar phenomenon can be seen with a plasma processing apparatus of such a system as shown in FIG. 9 in which a high frequency electric power is supplied to an opposite electrode 21 and also with a plasma processing apparatus of such a system as shown in FIG. 10 in which a high frequency electric power is supplied to a substrate electrode 9 thereby to generate plasma.